SPT3: Lysates

The transcription of many RNA polymerase II-dependent genes requires Spt3, a member of the S. cerevisiae SAGA complex. Transcription from delta sequences, the long terminal repeats that flank yeast Ty elements, requires the yeast SPT3 gene. Spt3 and Spt20 work together to recruit TATA-box binding protein (TBP) to the core promoter allowing TBP to bind to SAGA-dependent promoters. Null mutations in the Spt3 gene cause defects in sporulation, diploid filamentous growth, and haploid invasive growth, indicating that Spt3 has an important role in both mating and development pathways in yeast. At the promoters of some genes including yeast HO, HIS3 and TRP3 genes, Spt3 inhibits binding of TBP, resulting in reduced transcription. This repressive effect of Spt3 can be overcome by another member of the SAGA complex, GCN5, which promotes the formation of a TBP/TFIIA complex by histone acetylation.